单项选择题
A.is good for long term preserving since most insulation is organic and contains some amount
B.lowers the insulation value and is a common cause of fault grounds in idle machines
C.will enhance insulation resistance only if it is fresh water and contains no salt
D.reduces the amount of current supplied or drawn by the machine so horsepower is limited
单项选择题 When voltage and current developed in an AC circuit reach their peak values at the same time, the power factor is （）
单项选择题 While paralleling two AC generators using synchronizing lamps only, both lamps will go dark when the generators are （）.
单项选择题 Electric circuits are protected against overloads and short circuits by means of a/an （）.